The present invention relates to the assembly of sheets of glass and/or plastic materials for forming a laminated glazing. More particularly, the invention concerns the assembly of the aforesaid elements by calendering; that is to say by passing these elements between pinching rollers.
Further still, the invention relates to an apparatus for assembling a substrate, which can be either flat, or of simple or double curvature, which is monolithic or laminated, of glass or of plastic material, with a sheet or film of plastic material, for forming a safety glazing.
Although the invention may be utilized for the manufacture of a wide variety of laminated glazings, it will be described more particularly hereinafter in relation to the manufacture of a laminated safety glazing comprising a rigid, monolithic or laminated substrate, covered with a flexible sheet of plastic material, conferring the desired safety features. Such a glazing is, for example, described in French Pat. Nos. 2,187,719 and 2,251,608 and in Belgian Pat. No. 856,398.
The assembly of these laminated glazings is generally carried out by a preliminary pressing of the elements, by calendering, and if need be, followed by an autoclave cycle to improve the adherence between the elements of the laminate.
When the laminated glazing is flat, or when it has a simple curvature, the calendering can be done by passing the elements to be assembled between two cylindrical rollers covered with a suitable elastic material or even between two enlargeable rollers made of rubber. This operation generally poses no problems since it is easy in these two cases to apply uniform pressure on the entire surface of the assembled elements of the glazing.
On the other hand, when the laminated glazing has a double curvature, it becomes very difficult to obtain a homogeneous assembly of the elements over their entire surface.
There is a known apparatus with pressure rollers in which the rollers are equipped, on a length corresponding at least to the width of the sheets to be pressed, with a covering of an elastic material such as rubber, the inner space of this flexible covering being filled with a fluid under pressure. In such an apparatus, the roller acting on the concave side of the glazing takes on during operation the shape of a cigar following the transversal curvature of the glazing. Thereby, the linear speed at the periphery of the covering varies from point to point. Creases can therefore form on the sheet or film of plastic material applied by this roller to the substrate.
Another known apparatus exists in which the rollers are replaced by two superposed sets of wheels placed side by side, each of their positions being regulated independent of the other, to obtain the desired transversal curvature. Although this apparatus may be suited for the manufacture of a laminated glazing wherein the two outer sides are made of rigid elements, such as two sheets of glass, it is not adapted for the assembly of a flexible sheet with a rigid substrate, since it cannot provide a homogeneous adherence of such elements due to the formation of numerous air bubbles in the grooves corresponding to the spaces between two adjacent wheels acting against the flexible sheet.